Field of Disclosure
The disclosure relates to wireless power transfer (WPT), and more specifically to improving WPT between WPT devices.
Related Art
Wireless power transfer (WPT) is a technology integrated into a variety of devices which require frequent battery recharging. For example, mobile devices such as smartphones, laptops, tablets, and peripheral devices such as wireless headsets, all have batteries that require recharging, sometimes on a daily basis. A device equipped with WPT can be charged without requiring the device to be plugged directly into a power source. As long as the WPT-enabled device remains in proximity to a WPT charger, the WPT-enabled device will continuously charge, assuming the battery is capable of taking additional charge. In this way, it is possible for an end user to use a WPT-enabled device, such as a laptop, which remains relatively stationary during ordinary operation, while eliminating all power cords, adapters, and outlets that would otherwise be necessary for operation. Therefore, WPT has been heralded not only as a convenience, but also as a “green” technology, in that the utility of several power cords can be consolidated into a single WPT charger serving multiple WPT-enabled devices.
The WPT charger and the WPT-enabled device employ inductive coupling between one another to charge wirelessly. The WPT charger generates a magnetic field by driving current through a coil. The WPT-enabled device utilizes power harvesting circuitry coupled to a complementary coil to deliver power to a rechargeable battery. The WPT-enabled device must regulate this power to not exceed the power handling capabilities of the battery load. The WPT-enabled device and the WPT charger are coupled through their respective coils, such that a mutual inductance and capacitance is formed between the devices. The mutual inductance between the devices is a result of loose coupling between the coils, that is, a mutual inductance having a coupling factor less than 0.5, while the mutual capacitance results from the separation between the conductive coil surfaces. The efficiency of the WPT is dependent on this mutual inductive as well as capacitive coupling and the resonant frequency characteristics of each device.
The disclosure will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.